Towards a new reference ground motion prediction equation for Italy: update of the Sabetta–Pugliese (1996)

A revised Italian strong motion archive has become available since July 2007,
including all the records of the strongest events occurred from 1972 to 2004. It contains
the uncorrected and corrected accelerograms and the metadata relevant to seismic events,
recording stations and instruments added after a careful revision. The availability of this
archive allowed us to perform a first step towards an update of the reference ground motion
prediction equations for Italy, which were evaluated by Sabetta and Pugliese in (Bull Seismol
Soc Am 77:1491–1513, 1987), for peak ground acceleration and velocity, and subsequently
extended to the 5% damped pseudovelocity response spectra in 1996. A subset with the 27
major earthquakes occurred in Italy from 1972 to 2002, in the magnitude range 4.6–6.9,
was extracted and 235 good quality waveforms were selected, recorded at distances up to
183 km. The goodness of fit of the Sabetta and Pugliese (Bull Seismol Soc Am 86:337–352,
1996) model was explored using two independent statistical approaches (Spudich et al. Bull
Seismol Soc Am 89:1156–1170, 1999 and Scherbaum et al. Bull Seismol Soc Am 94:2164–
2185, 2004). The results obtained show that the Sabetta and Pugliese (Bull Seismol Soc Am
77:1491–1513, 1987) does not adequately fit the new strong-motion data set, for its small
standard deviation and its non-zero bias. In particular, the most noteworthy result is that the
Sabetta and Pugliese (Bull Seismol Soc Am 77:1491–1513, 1987) over-predicts peak ground
acceleration and velocity at rock sites. New coefficients for the prediction of horizontal peak
ground acceleration, peak ground velocity and acceleration response spectra, adopting the
same functional form in Sabetta and Pugliese (Bull Seismol Soc Am 77:1491–1513, 1987),
were then evaluated in order to fit the new data set. This paper illustrates the steps made to
update the existing ground motion prediction equations for Italy, discusses their limitations
and provides the basis for future developments.